Re: [PATCH rdma-next v3 2/2] RDMA/umem: block plain userspace memory registration under CoCo bounce

[Jiri Pirko <jiri@resnulli.us>]

Sun, May 17, 2026 at 06:17:12PM +0200, leon@kernel.org wrote:
>On Sun, May 17, 2026 at 04:13:11PM +0200, Jiri Pirko wrote:
>> From: Jiri Pirko <jiri@nvidia.com>
>> 
>> When a device requires DMA bounce buffering inside a Confidential
>> Computing guest, __ib_umem_get_va() cannot work. The DMA mapping layer
>> redirects all mappings through swiotlb bounce buffers, so the device
>> receives DMA addresses pointing to bounce buffer memory rather than
>> the user's pages. Since RDMA devices access registered memory directly
>> without CPU involvement, there is no opportunity for swiotlb to
>> synchronize between the bounce buffer and the original pages.
>> 
>> The registration would already fail later on, since the umem mapping
>> is requested with DMA_ATTR_REQUIRE_COHERENT and gets rejected under
>> is_swiotlb_force_bounce() with -EIO. Fail early with -EOPNOTSUPP
>> instead, so the user gets a specific error code to react to.
>> 
>> Signed-off-by: Jiri Pirko <jiri@nvidia.com>
>> ---
>> v1->v2:
>> - updated patch description with mention of DMA_ATTR_REQUIRE_COHERENT
>> ---
>>  drivers/infiniband/core/umem.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
>> index eb1de32bab9d..b32bc2a5d7d0 100644
>> --- a/drivers/infiniband/core/umem.c
>> +++ b/drivers/infiniband/core/umem.c
>> @@ -167,6 +167,9 @@ static struct ib_umem *__ib_umem_get_va(struct ib_device *device,
>>  	int pinned, ret;
>>  	unsigned int gup_flags = FOLL_LONGTERM;
>>  
>> +	if (device->cc_dma_bounce)
>> +		return ERR_PTR(-EOPNOTSUPP);
>> +
>
>The series looks reasonable, but I cannot apply it yet because  
>`__ib_umem_get_va()` has not been merged.

Correct. Cover letter says:
based on top of:
https://lore.kernel.org/all/20260517063006.2200680-1-jiri@resnulli.us/